1. Field of the Invention
The present invention relates to a lens barrel which includes barrier blades configured to open and close a front surface of a photographic lens, mounted on an imaging apparatus such as a camera, to protect the photographic lens.
2. Description of the Related Art
In a retractable-lens camera, which compactly retracts a lens barrel when the camera is carried and extends the lens barrel to move a photographic lens to an appropriate position when the camera is used, various lens barrier mechanisms have been proposed in which barrier blades cover the front surface of the lens when the lens barrel is in its retracted position and the barrier blades are retracted from the front surface of the lens when the camera is in use.
In such a barrier mechanism, the number of barrier blades which constitute the barrier can be selected depending on the effective optical path range of an optical system and the diameter of a lens barrel to effectively cover the front surface of a lens.
This is because there is a limitation on the dimension of the blade which can be stored in a blade storage portion defined by the difference between the diameter of the lens barrel and the effective optical path range of the optical system. Accordingly, with regard to the lens barrels with the same diameter, a larger number of barrier blades are needed as the effective optical path range of the optical system becomes larger.
Accordingly, it is general that a pair of barrier blades is provided to have a bilateral point symmetric relation and each barrier blade covers half of the effective optical path range of the optical system.
However, users tend to demand a zoom lens with a high magnification and a short focal length at the wide-angle end. Thus, the effective optical path range of the front surface of the lens and the optical path range in a space occupied by the barrier in the optical axis direction are considerably widened.
Even though the number of blades constituting the barrier increases to satisfy that demand, the barrier may be thickened in the optical axis direction due to the increase in number of blades. Then, in the space in the optical axis direction, the effective optical path is widened, and the blade storage portion may be narrowed. As a result, the effect of increasing the number of blades may be reduced, so that the space for the barrier in the optical axis direction may be extremely thickened.
Therefore, as a barrier for a lens of a wide-angle system having a short focal length, Japanese Patent Application Laid-Open No. 2007-102086 discusses a technique that decreases the thickness and the size of the barrier.
In the technique discussed in Japanese Patent Application Laid-Open No. 2007-102086, a blade having the largest amount of movement is disposed to be closest to the photographic lens and a second blade is provided with a pair of transmission portions to be pushed by the blade having the largest amount of movement at both its closed and opened sides.
Further, a third blade is provided with a pair of transmission portions to be pushed by the second blade at both its closed and opened sides.
Furthermore, the blade having the largest amount of movement and the third blade are each formed of a metallic sheet to be thin in thickness.
Furthermore, as the transmission portion, the blade having the largest amount of movement is provided with an upward bent portion which is bent in the direction opposite to the lens along the optical axis direction. Further, the third blade is provided with an upward bent portion which is bent toward the lens (the direction toward the imaging plane) along the optical axis direction. Then, since the transmission portion is formed by the upward bent portion, the second blade is formed as a component which is molded from plastic and is formed to be slightly thick.
This is because the upward bent portion, which is bent toward the lens (the direction toward the imaging plane) along the optical axis direction, is provided in either the blade having the largest amount of movement or the second blade. Thus, since there is concern that the lens may be scratched when the upward bent portion passes on the lens, the upward bent portion is not provided in the range overlapping the front lens surface as viewed on the projection plane.
For this reason, in the technique discussed in Japanese Patent Application Laid-Open No. 2007-102086, the second blade is molded from plastic.